


Habits are Easy to Start

by OnyxSinz (OnyxianDrake)



Series: Dark Love [1]
Category: Undertale (Video Game)
Genre: Alternate Universe - Dreamtale (Undertale), Dreamtale Nightmare Sans/Killer Sans (Undertale), Knotting, M/M, Power Imbalance, Rape/Non-con Elements, Restraints, Soul Sex, Tentacles, Undertale Multiverse, dub-con
Language: English
Status: Completed
Published: 2020-11-02
Updated: 2020-11-02
Packaged: 2021-03-08 22:08:53
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 1,487
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/27354001
Author URL: https://archiveofourown.org/users/OnyxianDrake/pseuds/OnyxSinz
Summary: Nightmare needs to test Killer's loyalty, and feed. Why not combine the two?
Relationships: NightKiller, Sans/Sans (Undertale)
Series: Dark Love [1]
Series URL: https://archiveofourown.org/series/1997761
Comments: 2
Kudos: 82





	Habits are Easy to Start

**Author's Note:**

> This is from Day 29 of my Kinktober 2020 piece.

Killer didn’t trust whatever this was  _ one bit _ . He had his knife in hand, a grin plastered on his face like always, but the entire feeling of the room was  _ off _ . Nightmare was  _ too _ quiet, sitting on his throne, staring Killer down. Wisely, he kept his distance, knowing too well the reach of those tentacles, despite knowing he had to approach sooner or later.

“Ya called, boss?”

Breaking the silence felt like a crime in itself, and Killer knew very well if Nightmare wanted him dead, he’d already be dust on the floor. Not that it was much consolation, considering he’d been beat to within an inch of his life for just nicking the bastard with his knife. Killer hadn’t even known who the fuck Nightmare was then, and he still wasn’t sure why he bothered to agree to his demands.

“I did. Come here.”

Nightmare’s voice was cool, unbothered. Despite the hollow feeling in his chest, Killer knew well enough when to be a little on edge. Ignoring the uneasy prickle of distrust, he stepped forward, slowly closing the distance until he was a good two yards from the throne. Although he was less concerned about the throne, and more concerned about the fact he still couldn’t read Nightmare.

Here Killer thought he’d actually begun to understand how to read him, leaving him without ground to stand on to figure out what the hell Nightmare wanted him for-!

Killer froze when Nightmare’s tentacles moved, acutely aware of the specific one extending out to pull away his soul from where it hovered it front of his chest. The frigid aura Nightmare gave off made him shiver, not daring to move even as one tentacle managed to cinch his hands behind his back. His knife was gone, but that didn’t matter so much as he tried to find an explanation for why Nightmare wanted his soul.

“Pretty sure ya destabilized it recently enough,” Killer coughed, not reacting to the glance Nightmare gave him, “still ain’ feelin’ nothin’, don’t need it again yet-”

“That’s not why you’re here,” Nightmare hummed as he leaned back, Killer’s soul now hovering in his hand.

The freezing press of Nightmare’s thumb to his soul had Killer gasping as he jolted in the tentacle’s hold, “W-what the fuck?” Killer snapped. “Why am I here then?”

Nightmare smirked, standing from the throne as he walked closer to Killer. Killer leaned away as best he could from Nightmare, only kept in place by the tentacle restraining him.

“You’re unfortunate, being my only henchman for the moment,” Nightmare purred, “especially when I need to feed at the same time I was planning to have you prove your loyalty to me.”

“T-that doesn’t explain why you’re messing with my soul-!”

Killer gritted his teeth with a hiss as he turned his skull away, feeling a discomforting warmth beginning to prickle through his bones and in his soul. It amplified the chill of Nightmare’s fingers that much more, as they squeezed the target shaped soul.

“There are many ways for me to feed, and just as many ways for you to prove your loyalty. Unfortunately, I’ve grown bored of the AUs for the moment, and you’re the closest in reach to help me with that predicament…”

The room shifted, leaving Killer’s vision spinning as he tried to readjust to the surroundings, going from the familiar throne room to one he’d never seen. It was a bedroom. That was easy enough to tell if the large bed was anything to go by. It was just as easy to guess it was Nightmare’s, because it sure as hell wasn’t Killer’s.

“Now,” Nightmare’s voice startled Killer out of his daze, “are you going to prove your loyalty to me, or should I cut you loose before I regret saving you from that forsaken AU?”

...Killer wasn’t sure he heard Nightmare right, but the intent stare, blank and waiting for an answer said otherwise. He had a  _ choice? _ Of all things, being given an out wasn’t one of them. Then again, until now, he didn’t expect Nightmare to molest his soul, but that had already been proven contradictory. All signs were pointing to Nightmare planning on whatever loyalty test this was to be sexual, which didn’t seem  _ unappealing _ .

It really felt like it was a damned if he did, damned if he didn’t scenario, but Killer couldn’t care less. Slowly his grin returned with a sneer.

“Are ya gonna get started or hang me out to dry? I’m waitin’.”

Nightmare’s socket narrowed, and Killer briefly wondered if he just asked for a death sentence before he was very suddenly knocked breathless as he was flung onto the bed.

“Strip.”

Killer snickered as he sat up, unabashedly removing his jacket and shirt, but he faltered with a grunt when his soul was squeezed. He shuddered, narrowing his sockets towards Nightmare, who smirked right back with a raised brow.

“You seem awfully eager now.”

Killer raised a brow, “Should I not be?”

Nightmare was quiet for a moment, Killer simply grinned seeing the faintest blue blush building on his cheeks as Killer kicked off his shorts. He didn’t fight the tentacles that pinned him, just raised a brow when Nightmare seemed contemplative. It lasted barely a moment, before Nightmare hit him with an overwhelming demand to summon his magic.

“F-fuck, wait-”

Killer could already feel the emotions prickling in his soul as Nightmare pulled away his influence, what was keeping it locked all away so perfectly. He gasped wetly as Nightmare was suddenly straddling him, naked as well, with his own ecto summoned. Couldn’t even appreciate the curves Nightmare had, not with the liquid hate pouring more intensely from his sockets as he went still, breath hitching.

“Good,” Nightmare purred, Killer moaning weakly as the wet warmth of Nightmare’s walls slipped over his cock until Nightmare was seated flush against him.

He hated the whimper that slipped out when the control further broke the destabilizing magic keeping his emotions away, struggling as Nightmare moaned above him.

“B-boss- too much-” he hiccuped, refusing to cry out or sob.

“You’re doing fine,” Nightmare purred, drawing another strangled moan out of Killer as Nightmare lifted himself up and settled right back down with a wet noise, a proper blush on his dark cheekbones.

Killer felt like he would strongly disagree if he could manage words anymore, panting and trying not to make too much noise. Too much was being demanded of his soul, everything feeling fuzzy and agonizing between his conflicted emotions and physical pleasure.

“Just a little more...your guilt is just what I needed~”

A sharp tug, a demand from Nightmare to his soul, had Killer soundlessly screaming as he came, feeling Nightmare clench down around him with a softer moan in return. All the sensations left Killer dizzy, panting and barely aware of the single eyelight just inches from his face. Slowly, the familiar disconnect settled back into his soul, Nightmare’s cold magic forcing his own into a numb echo of everything he just felt.

“Are you back in your skull yet, dumbass?” Nightmare grumbled, startling Killer briefly.

They were still in the large, and frankly very comfortable, bed. It was...surprising, to say the least. Killer expected to be alone, or dumped in his own room already to clean himself up. As he blinked away the blur to his vision, it became more obvious that Nightmare was still on top of him, which was...confusing. Killer felt sluggish mentally as he pulled himself together, barely able to move to sit up before Nightmare was hissing at him.

“Don’t you fucking dare!”

Killer stopped, brow raised as a brighter blush bloomed oved Nightmare’s face, and he slowly realized both their ectos were still summoned...and they were still very connected. Nightmare seemed to know where his mind was going, and Killer couldn’t help the grin that was growing on his face from amusement.

“Don’t say a fucking word-!”

“Little stuck there boss?”

“Fuck you.”

“...pretty sure you just did.”

Killer snorted before he swore when Nightmare tried pulling himself off, grappling to keep him from moving again as he glared up at his boss. Nightmare seemed just as discomforted by the painful tug, but seemed to attempt to act smug regardless.

“This is your fault, I didn’t plan to get stuck like this, I still have work to do.”

All he could do was shrug, still grinning as Nightmare frowned down at him, “This better not happen next time.”

Killer blinked at that, sockets wide, “...You actually plan on there being a next time?”

Nightmare smirked, Killer still mildly surprised as he leaned down, elbows placed on either side of Killer’s head. It was hard not to break the moment by groping the very tempting breasts pressed to his ribs, but he stayed focused on Nightmare’s face.

“Of course, you belong to me, after all.”


End file.
